Measuring the landward gulf stream front variability off Cape Hatteras with HF radar

Abstract

A decade of coastal ocean radar surface current observations of the Gulf Stream off Cape Hatteras, NC have been collected that offer to provide key new insights into the temporal and spatial variability of the Gulf Stream in this region. The Gulf Stream is believed to have a profound influence on the complex current dynamics off of Cape Hatteras, NC that result from the convergence of many different water masses in the region. Although essential to understanding oceanography off the NC coast, and to linkages beyond the region, Gulf Stream variability in this area has been difficult to quantify because of the challenge involved in obtaining observations of consistent spatial and temporal resolution over long time periods. Analysis of Long Range Seasonde Coastal Ocean Radar (Codar) ocean surface current measurements from two sites in NC may provide estimates of the landward Gulf Stream edge over a nearly continuous ten-year period. Radar surface current measurements are made hourly, more frequently than satellite measurements, and provide more consistent coverage of the Gulf Stream than many historical measurement techniques. The 5MHz radars typically make surface current measurements across the entire cyclonic shear zone on the landward side of the Gulf Stream. These measurements may provide methods to define Gulf Stream location, width, transport and variability of these properties over time and alongshore, providing insights into the current dynamics off Cape Hatteras, NC. We here present a method to identify the landward Gulf Stream position and width of the cyclonic shear zone from radar surface currents. The method of front detection developed associates the landward Gulf Stream front with maxima in the radial current shears. Maxima are chosen within regions of consistent coverage over the time period sampled. The locations where the Gulf Stream first enters and exits the radar coverage area are apparent as large radial speeds measured by the radar, and one bearing is chosen from each region for analysis. However in a region between these two zones the Gulf Stream is perpendicular to the radials and the method can not be used. This method can be applied to each of three radars located in the vicinity of Cape Hatteras.